At the higher systems level, microinverter design calls for real-time execution of a number of precise algorithms for efficient DC-AC conversion, circuit protection and PV panel power optimization through maximum power-point tracking (MPPT). MPPT is essential to maintain the optimum panel loading required to sustain the best possible power output from the panel served by each microinverter module.

The key algorithms for these tasks are typically available in proven software libraries that complement digital signal controllers and microcontrollers with integrated peripherals such as the Analog Devices ADuC7128 microcontroller, the Microchip Technology dsPIC33F digital signal controller, and Texas Instruments' TMS320F28x digital signal controller, among others. The availability of integrated peripherals, including analog to digital converters (ADCs) and pulse-width-modulated outputs (PWMs), allow these controllers to directly sense inputs and precisely control power MOSFETs in bridge circuits, improving overall efficiency while reducing parts count and module size.

Exposed to the environment, the microinverter requires the same kind of circuit protection required in central inverters but with even more reliable circuit components able to withstand extremes in temperature and humidity. At the same time, microinverter design requires the smallest, most cost-effective BOM possible to minimize cost, weight, and volume in the final modules attached to each PV panel. Consequently, some of the most efficient inverter multi-stage topologies with relatively high BOM counts might not be practical. Instead, microinverter designs tend to rely on simpler one- or two-stage inverter topologies.

Single-stage microinverters boost the panel voltage and shape the AC waveform output in a single stage. This approach results in the lowest possible component count, while simplifying isolation. Its disadvantages include high voltage ratings on both the primary side switches and the secondary side diode, as well as high amplitude ripple current on the input, which would lead to power loss without the use of large electrolytic capacitors on the microinverter input. This electrolytic capacitor required for power decoupling between the PV panel and grid tends to be the limiting component for module reliability. Ripple current in the electrolytic capacitor produces heat, raising temperature in this component and further reducing its lifespan.

The use of an interleaved flyback converter topology shown in Figure 2 helps improve the lifespan of the capacitor by reducing ripple current. The interleaving action of this approach also reduces current total harmonic distortion of the output current. In a grid-tied installation, engineers also need to measure grid characteristics to properly synchronize microinverter output to the grid and handle islanding, or isolation of the module in the event of loss of connection to the grid due to external events such as power failures.

Along with this single-stage design, the two-stage topology is a suitable candidate for microinverter circuits . Built around an intermediate high-voltage DC bus, this approach boosts input PV voltage to the intermediate-bus voltage. A conventional pulse-width modulation inverter then puts the final shaped AC waveform on the output. This approach results in significantly lower input ripple current at the PV input, permitting use of lower capacitance components such as high reliability film capacitors rather than electrolytic capacitors.

<quoted text>"avoid failures on a large scale"?"do a very good job"?Care to give concrete statistics to back this up?Or are you just another shill for the quasi-industry?

Solar panels produce direct current at a voltage that depends on the module's design and the lighting conditions. Modern panels using 6" cells normally contain 60 cells and produce a nominal 30 volts.[4] For conversion into AC, panels are connected in series to produce effectively a single large array with a nominal rating of around 300 to 600 VDC. The power is then run to an inverter, which converts it into standard AC voltage, typically 240VAC/60 Hz for the North American market, or 220VAC/50 Hz in Europe.[5]

The main problem with this "string inverter" approach is that the string of panels will act as if it was a single larger panel rated to the worst of the individual panels within it. For instance, if one panel in a string has 5% higher resistance due to a minor manufacturing defect, the string as a whole will perform 5% worse (or thereabouts). This situation is dynamic; if a panel is shaded its output drops dramatically, affecting the output of the string as a whole even if the other panels are not shaded. Even slight changes in orientation can cause mis-matches in output in this fashion.

Additionally, the efficiency of a panel's output is strongly affected by the load the inverter places on it. In order to maximize production, inverters use a technique known as maximum power point tracking (MPPT) to ensure optimal collection by adjusting the applied load. However, the same issues that cause output to vary from panel to panel affect the proper load that the MPPT system should apply. If a single panel is operating at a different point, a string inverter can only see the overall change, and will move the MPPT point to match. This will result in not just the losses from the shadowed panel, but all of the other panels as well. Shading of as little as 9% of the entire surface array of a PV system can, in some circumstances, lead to a system-wide power loss of as much as 54%.[6][7]

A further problem, although minor, is that string inverters come in a limited selection of power ratings. This means that a given array will normally upsize the inverter to the next-largest model over the rating of the panel array. For instance, a 10-panel array of 2300 W might have to use a 2500 or even 3000 W inverter, paying for conversion capability it cannot use. This same effect makes it difficult to change array sizes over time, adding power when funds are available. With micro-inverters, different ratings of solar panels can be added to an array even if they don't match the original types.

Other challenges associated with centralized inverters include the space required to locate the device, as well as heat dissipation requirements. Large central inverters are typically actively cooled. Cooling fans make noise, so location of the inverter relative to offices and occupied areas must be considered.

Micro-inverters are small inverters rated to handle the output of a single panel. Modern grid-tie panels are normally rated between 220 and 245 Watts, but rarely produce this in practice, so micro-inverters are typically rated between 190 and 220 W. Because it is operated at this lower power point, many design issues inherent to larger designs simply go away; the need for a large transformer is generally eliminated, large electrolytic capacitors can be replaced by more reliable thin-film capacitors, and cooling loads are so reduced that no fans are needed. Mean time between failures (MTBF) are quoted in the hundreds of years.

More importantly, a micro-inverter attached to a single panel allows it to isolate and tune the output of that panel. A dual micro-inverter does this for two panels. For example, in the same 10-panel array used as an example above, with micro-inverters any panel that is underperforming will have no effect on the panels around it. In that case, the array as a whole will produce as much as 5% more power than it would with a string inverter. When shadowing is factored in, if present, these gains can become considerable, with manufacturers generally claiming 5% better output at a minimum, and up to 25% better in some cases.

Micro-inverters produce grid-matching power directly at the back of the panel. Arrays of panels are connected in parallel to each other, and then to the grid feed. This has the major advantage that a single failing panel or inverter will not take the entire string offline. Combined with the lower power and heat loads, and improved MTBF, it is suggested that overall array reliability of a micro-inverter-based system will be significantly greater than a string-inverter based one. This assertion is supported by longer warranties, typically 15 to 25 years, compared with 5 or 10 year warranties that are more typical for string inverters. Additionally, when faults occur, they are identifiable to a single point, as opposed to an entire string. This not only makes fault isolation easier, but unmasks minor problems that might never become visible otherwise - a single underperforming panel may not affect a short string's output enough to be noticed

Come on Ace, is copy and paste your best shot????What you have here is a hodge podge of bullshitwhich is probably 5 or more years old.... So let us catch you up to the year 2012....

Sequenced inverters eliminate the need for electrolytic capacitors, optocouplers, varistors and cooling fans which are crucial for units operating with micro inverters.... Sequenced inverters use iron-and-copper inductors and industrial level semiconductors which offer an equal level throughout the system and eliminate the need for high input storage within the grid.... These inverters are on average 10% cheaper in cost and plug and play installs unlike your micro inverters which cost a small fortune...

As stated before, the sequenced inverter is also the only one to offer III Phase 208 which those micro inverters can't handle....

Come on Ace, is copy and paste your best shot????What you have here is a hodge podge of bullshitwhich is probably 5 or more years old.... So let us catch you up to the year 2012....Sequenced inverters eliminate the need for electrolytic capacitors, optocouplers, varistors and cooling fans which are crucial for units operating with micro inverters.... Sequenced inverters use iron-and-copper inductors and industrial level semiconductors which offer an equal level throughout the system and eliminate the need for high input storage within the grid.... These inverters are on average 10% cheaper in cost and plug and play installs unlike your micro inverters which cost a small fortune...As stated before, the sequenced inverter is also the only one to offer III Phase 208 which those micro inverters can't handle....

The maroons are frantically searching google now to figure out what you said.

Expect another cut and paste for wikipedia with abso-four-king-lutely no first hand knowledge of the subject.

<quoted text>The maroons are frantically searching google now to figure out what you said.Expect another cut and paste for wikipedia with abso-four-king-lutely no first hand knowledge of the subject.These dopes are getting boring...

Lets hope so....If they should decide to cut and paste, lets see if any of it refers back to pulse amplitude modulation and no need for rectifiers...

Is this our little group of community college friends fromBum Fck, Tennessee?????

Oh my, the amusement of community college wizards....But I will give you a D+ for the effort in finding a just released micro inverter which works on DC to AC and produces the 208 which I specified....

However you failed in researching my comments in that the Sequenced inverters eliminate the DC making the entire grid straight AC from the module to the grid, and YES, the Sequenced inverters are the only ones to produce 208 in this grid.... Had you looked a bit further you also would have found that micro inverters have been producing 208 for years but NOT in a solid AC grid....

Manufactures of AC grid systems have been using synchronous inverters which allow for peak efficiencies of over 94% whereasthe Sequenced inverters are capable of efficiencies in the 99% range at a cheaper cost....

<quoted text>Oh my, the amusement of community college wizards....But I will give you a D+ for the effort in finding a justreleased micro inverter which works on DC to AC and producesthe 208 which I specified.

Just released ?? Where have you been. I have been installing these for better than two years.

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